In oil and gas wells, it is conventional to pass a number of concentric tubes or casings down the well. An outermost casing is fixed in the ground, and the inner casings are each supported from the next outer casing by casing hangers which take the form of interengaging internal shoulders on the outer casing and external shoulders on the inner casing.
Such casing hangers are fixed in position on each casing. There are however applications where a fixed position casing hanger is unsatisfactory, because the hang-off point of one casing on another may require to be adjusted.
The invention has particular application to tubing hangers, especially tensioned tubing hangers.
Where drilling wellheads have to accommodate a casing with an undetermined hang-off point, it has been known to use casing slip-type support mechanisms.
It is also known from European patent number 0 251 595 to use an adjustable landing ring on a surface casing hanger to accommodate a space-out requirement when the casing is also landed in a surface wellhead.